holy shit everything passes

packages/svelte/src/internal/client/reactivity/async.js

@@ -303,6 +303,9 @@ export function wait(blockers) {
 	return Promise.all(blockers.map((b) => b.promise));
 }
 
+/**
+ * @returns {(skip: boolean) => void}
+ */
 export function increment_pending() {
 	var boundary = /** @type {Boundary} */ (/** @type {Effect} */ (active_effect).b);
 	var batch = /** @type {Batch} */ (current_batch);
@@ -311,8 +314,8 @@ export function increment_pending() {
 	boundary.update_pending_count(1, batch);
 	batch.increment(blocking);
 
-	return () => {
+	return (skip) => {
 		boundary.update_pending_count(-1, batch);
-		batch.decrement(blocking);
+		batch.decrement(blocking, skip);
 	};
 }

packages/svelte/src/internal/client/reactivity/batch.js

@@ -441,7 +441,7 @@ export class Batch {
 				// Re-run async/block effects that depend on distinct values changed in both batches
 				const others = [...batch.current.keys()].filter((s) => !this.current.has(s));
 				if (others.length > 0) {
-					current_batch = batch;
+					batch.activate();
 
 					/** @type {Set<Value>} */
 					const marked = new Set();
@@ -459,9 +459,9 @@ export class Batch {
 						}
 
 						// TODO do we need to do anything with the dummy effect arrays?
-
-						batch.deactivate();
 					}
+
+					batch.deactivate();
 				}
 			}
 
@@ -483,14 +483,14 @@ export class Batch {
 	}
 
 	/**
-	 *
 	 * @param {boolean} blocking
+	 * @param {boolean} skip - whether to skip updates (because this is triggered by a stale reaction)
 	 */
-	decrement(blocking) {
+	decrement(blocking, skip) {
 		this.#pending -= 1;
 		if (blocking) this.#blocking_pending -= 1;
 
-		if (this.#decrement_queued) return;
+		if (this.#decrement_queued || skip) return;
 		this.#decrement_queued = true;
 
 		queue_micro_task(() => {

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -161,6 +161,13 @@ export function async_derived(fn, label, location) {
 		const handler = (value, error = undefined) => {
 			if (DEV) current_async_effect = null;
 
+			if (decrement_pending) {
+				// don't trigger an update if we're only here because
+				// the promise was superseded before it could resolve
+				var skip = error === STALE_REACTION;
+				decrement_pending(skip);
+			}
+
 			if (error === STALE_REACTION || (effect.f & DESTROYED) !== 0) {
 				return;
 			}
@@ -198,10 +205,6 @@ export function async_derived(fn, label, location) {
 				}
 			}
 
-			if (decrement_pending) {
-				decrement_pending();
-			}
-
 			batch.deactivate();
 		};
 

packages/svelte/tests/runtime-runes/samples/async-linear-order-same-derived/_config.js

@@ -2,12 +2,6 @@ import { flushSync, tick } from 'svelte';
 import { test } from '../../test';
 
 export default test({
-	// TODO this test fails, because effects get scheduled on a batch that
-	// has already committed. there are some subtle timing issues
-	// that are exposed by the more rigorous implementation in this
-	// PR, and I'm still figuring out how to fix them
-	skip: true,
-
 	async test({ assert, target }) {
 		const [a, b, shift, pop] = target.querySelectorAll('button');